US 20060003510 A1
A dislocation region is formed by implanting a light inert species, such as hydrogen, to a specified depth and with a high concentration, and by heat treating the inert species to create “nano” bubbles, which enable a certain mechanical decoupling to underlying device regions, thereby allowing a more efficient creation of strain that is induced by an external stress-generating source. In this way, strain may be created in a channel region of a field effect transistor by, for instance, a stress layer or sidewall spacers formed in the vicinity of the channel region.
1. A method, comprising:
providing a semiconductor region above a substrate;
forming a dislocation region in at least one of said substrate and said semiconductor region, said dislocation region enabling a relative motion on an atomic scale between said substrate and at least a portion of said semiconductor region; and
forming a stress-inducing region mechanically coupled to said semiconductor region, said stress-inducing region creating strain in said at least a portion of the semiconductor region.
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providing a second semiconductor region;
forming said dislocation region to enable a relative motion on an atomic scale between said substrate and at least a portion of said second semiconductor region; and
forming a second stress-inducing region mechanically coupled to said second semiconductor region, said second stress-inducing region creating a second strain in said at least a portion of the second semiconductor region, said second strain differing from said strain.
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21. A method, comprising:
implanting a light inert ion species through a semiconductor region into a substrate at a specified depth;
forming a transistor element above said specified depth, said transistor element having a drain region, a source region, a channel region comprised of said semiconductor region and a gate electrode structure; and
heat treating said substrate to form a dislocation region adjacent to said channel region, said dislocation region enabling a relative motion on an atomic scale between said substrate and at least a portion of said channel region.
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30. A semiconductor device, comprising:
a strained semiconductor region located above said substrate; and
a dislocation region formed between said substrate and said strained semiconductor region, said dislocation region enabling a relative motion on an atomic scale between said substrate and at least a portion of said strained semiconductor region.
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1. Field of the Invention
Generally, the present invention relates to the formation of integrated circuits, and, more particularly, to the formation of semiconductor regions of increased charge carrier mobility, such as a channel region of a field effect transistor, by creating strain in the semiconductor region.
2. Description of the Related Art
The fabrication of integrated circuits requires the formation of a large number of circuit elements on a given chip area according to a specified circuit layout. Generally, a plurality of process technologies are currently practiced, wherein, for complex circuitry, such as microprocessors, storage chips and the like, MOS technology is currently the most promising approach due to the superior characteristics in view of operating speed and/or power consumption and/or cost efficiency. During the fabrication of complex integrated circuits using MOS technology, millions of transistors, i.e., N-channel transistors and/or P-channel transistors, are formed on a substrate including a crystalline semiconductor layer. A MOS transistor, irrespective of whether an N-channel transistor or a P-channel transistor is considered, comprises so-called PN junctions that are formed by an interface of highly doped drain and source regions with an inversely doped channel region disposed between the drain region and the source region.
The conductivity of the channel region, i.e., the drive current capability of the conductive channel, is controlled by a gate electrode formed above the channel region and separated therefrom by a thin insulating layer. The conductivity of the channel region upon formation of a conductive channel, due to the application of an appropriate control voltage to the gate electrode, depends on the dopant concentration, the mobility of the charge carriers, and, for a given extension of the channel region in the transistor width direction, on the distance between the source and drain regions, which is also referred to as channel length. Hence, in combination with the capability of rapidly creating a conductive channel below the insulating layer upon application of the control voltage to the gate electrode, the conductivity of the channel region substantially determines the performance of MOS transistors. Thus, the reduction of the channel length, and associated therewith the reduction of the channel resistivity, renders the channel length a dominant design criterion for accomplishing an increase in the operating speed of the integrated circuits.
The continuing shrinkage of the transistor dimensions, however, entails a plurality of issues associated therewith that have to be addressed so as to not unduly offset the advantages obtained by steadily decreasing the channel length of MOS transistors. One major problem in this respect is the development of enhanced photolithography and etch strategies to reliably and reproducibly create circuit elements of critical dimensions, such as the gate electrode of the transistors, for a new device generation. Moreover, highly sophisticated dopant profiles, in the vertical direction, as well as in the lateral direction, are required in the drain and source regions to provide low sheet and contact resistivity in combination with a desired channel controllability. In addition, the vertical location of the PN junctions with respect to the gate insulation layer also represents a critical design criterion in view of leakage current control. Hence, reducing the channel length also requires reducing the depth of the drain and source regions with respect to the interface formed by the gate insulation layer and the channel region, thereby requiring sophisticated implantation techniques. According to other approaches, epitaxially grown regions are formed with a specified offset to the gate electrode, which are referred to as raised drain and source regions, to provide increased conductivity of the raised drain and source regions, while at the same time maintaining a shallow PN junction with respect to the gate insulation layer.
Since the continuous size reduction of the critical dimensions, i.e., the gate length of the transistors, necessitates the adaptation and possibly the new development of highly complex process techniques concerning the above-identified process steps, it has been proposed to also enhance device performance of the transistor elements by increasing the charge carrier mobility in the channel region for a given channel length, thereby offering the potential for achieving a performance improvement that is comparable with the advance to a future technology node while avoiding many of the above process adaptations associated with device scaling. In principle, at least two mechanisms may be used, in combination or separately, to increase the mobility of the charge carriers in the channel region. First, the dopant concentration within the channel region may be reduced, thereby reducing scattering events for the charge carriers and thus increasing the conductivity. However, reducing the dopant concentration in the channel region significantly affects the threshold voltage of the transistor device, thereby presently making a reduction of the dopant concentration a less attractive approach unless other mechanisms are developed to adjust a desired threshold voltage. Second, the lattice structure in the channel region may be modified, for instance by creating tensile or compressive stress to produce a corresponding strain in the channel region, which results in a modified mobility for electrons and holes, respectively. For example, creating tensile strain in the channel region increases the mobility of electrons, wherein, depending on the magnitude and direction of the tensile strain, an increase in mobility of 120% or more may be obtained, which, in turn, may directly translate into a corresponding increase in the conductivity. On the other hand, compressive strain in the channel region may increase the mobility of holes, thereby providing the potential for enhancing the performance of P-type transistors. The introduction of stress or strain engineering into integrated circuit fabrication is an extremely promising approach for further device generations, since, for example, strained silicon may be considered as a “new” type of semiconductor, which may enable the fabrication of fast, powerful semiconductor devices without requiring expensive semiconductor materials and manufacturing techniques.
Consequently, it has been proposed to introduce, for instance, a silicon/germanium layer or a silicon/carbon layer in or below the channel region to create tensile or compressive stress that may result in a corresponding strain. Although the transistor performance may be considerably enhanced by the introduction of stress-creating layers in or below the channel region, significant efforts have to be made to implement the formation of corresponding stress layers into the conventional and well-approved MOS technique. For instance, additional epitaxial growth techniques have to be developed and implemented into the process flow to form the germanium or carbon-containing stress layers at appropriate locations in or below the channel region. Hence, process complexity is significantly increased, thereby also increasing production costs and the potential for a reduction in production yield.
Thus, in other approaches, external stress created by, for instance, overlaying layers, spacer elements and the like is used in an attempt to create a desired strain within the channel region. However, the process of creating the strain in the channel region by applying a specified external stress suffers from a highly inefficient translation of the external stress into strain in the channel region, since the channel region is strongly bonded to the buried insulating layer in silicon-on-insulator (SOI) devices or the remaining bulk silicon in bulk devices. Hence, although providing significant advantages over the above-discussed approach requiring additional stress layers within the channel region, the moderately low strain obtained renders the latter approach less attractive.
In view of the above-described situation, there exists a need for an alternative technique that enables the creation of desired stress conditions in the transistor structure without requiring complex and expensive epitaxial growth techniques or variations of critical manufacturing steps.
The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an exhaustive overview of the invention. It is not intended to identify key or critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is discussed later.
Generally, the present invention is directed to a technique that enables the formation of a strained semiconductor region, in particular a strained channel region of a field effect transistor, in that a certain degree of mechanical decoupling is provided between the semiconductor region, or a portion thereof, and a substrate on which the semiconductor region is formed. To achieve the mechanical decoupling, at least to a specified degree, a dislocation region is formed that at least significantly weakens the bonding of the semiconductor region under consideration to the device region below the semiconductor region of interest so that any external stress transferred to the semiconductor region under consideration may effectively be translated into a corresponding strain, thereby significantly affecting the charge carrier mobility within the semiconductor region. Hereby, the stress created externally from the semiconductor region of interest may be supplied temporarily or permanently to correspondingly adjust, for instance, the performance of a field effect transistor by increasing the on-current of the transistor, substantially without negatively affecting the static characteristics thereof.
According to one illustrative embodiment of the present invention, a method comprises providing a semiconductor region above a substrate and forming a dislocation region in at least one of the substrate and the semiconductor region, wherein the dislocation region enables a relative motion on an atomic scale between the substrate and at least a portion of the semiconductor region. Moreover, a stress-inducing region is formed that is mechanically coupled to the semiconductor region, wherein the stress-inducing region creates strain, at least in that portion of the semiconductor region.
According to a further illustrative embodiment of the present invention, a method comprises implanting a light inert ion species through a semiconductor region into a substrate at a specified depth. Moreover, the method comprises forming a transistor element above the specified depth, wherein the transistor element has a drain region, a source region, a channel region comprised of the semiconductor region and a gate electrode structure. Finally, a heat treatment is performed with the substrate to form a dislocation region adjacent to the channel region, wherein the dislocation region enables a relative motion on an atomic scale between the substrate and at least a portion of the channel region.
In accordance with yet another illustrative embodiment of the present invention, a semiconductor device comprises a substrate, a strained semiconductor region located above the substrate and a dislocation region. The dislocation region is formed between the substrate and the strained semiconductor region, and enables a relative motion on an atomic scale between the substrate and at least a portion of the strained semiconductor region.
The invention may be understood by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals identify like elements, and in which:
While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.
Illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.
The present invention will now be described with reference to the attached figures. Various structures, systems and devices are schematically depicted in the drawings for purposes of explanation only and so as to not obscure the present invention with details that are well known to those skilled in the art. Nevertheless, the attached drawings are included to describe and explain illustrative examples of the present invention. The words and phrases used herein should be understood and interpreted to have a meaning consistent with the understanding of those words and phrases by those skilled in the relevant art. No special definition of a term or phrase, i.e., a definition that is different from the ordinary and customary meaning as understood by those skilled in the art, is intended to be implied by consistent usage of the term or phrase herein. To the extent that a term or phrase is intended to have a special meaning, i.e., a meaning other than that understood by skilled artisans, such a special definition will be expressly set forth in the specification in a definitional manner that directly and unequivocally provides the special definition for the term or phrase.
The present invention is based on the concept that strain may be created within a portion of interest of a semiconductor region by weakening the bonding of the portion of interest to a device region located below the portion of interest. Due to the decreased mechanical coupling of the semiconductor region to the lower lying device region or substrate, an externally-generated stress, which may be created by any appropriate means, such as sidewall spacers of a gate electrode structure, an etch stop layer for an interlayer dielectric and the like, may be highly efficiently transferred into the semiconductor region of interest, which may then correspondingly deform since the weakened bonding or the mechanical decoupling allows, to a certain degree, a relative motion between the particles forming the crystal lattice of the semiconductor region and the lower lying device region or substrate. Hereinafter, a region enabling a relative motion on an atomic scale of two device regions adjacent to this region is referred to as a dislocation region since it enables a certain dislocation of the two regions, which enclose the dislocation region. It should be noted that here the term “dislocation” is meant to describe a change in the relative position of a small volume element of one region with respect to a corresponding small volume element of an adjacent region, wherein the relative position change may correspond to a deformation, such as tensile deformation or strain, or compressive deformation or strain, rather than a uniform translation of one region in its entirety with respect to the other region. For example, a region comprising a plurality of voids having a size on the order of magnitude of nanometers, which is sandwiched by two device regions substantially without any voids, may be considered as a dislocation region, since the “nano-voids” enable a relative motion between the two substantially void-free regions on an atomic scale upon the influence of an external force, so that one or both of the substantially void-free regions may deform or strain. If the deformed or strained region is a substantially crystalline semiconductor region, the strain may result in a modified lattice spacing and therefore a modified charge carrier mobility.
With reference to the drawings, further illustrative embodiments of the present invention will now be described in more detail, wherein it is referred to field effect transistor devices that are to receive, at least partially, a dislocation region for creating strain in their respective channel regions to enhance the drive current capability of the devices, substantially without requiring the formation of complex stress-inducing layers within the channel region. It should be appreciated, however, that the principles of the present invention may be applied to any semiconductor region requiring an increase in charge carrier mobility by an externally-provided stress source. For instance, buried semiconductor lines comprising a doped crystalline semiconductor material may be formed in accordance with the present invention to have tensile or compressive strain for increasing their conductivity.
In other embodiments, the substrate 101 may represent a bulk semiconductor substrate, such as a bulk silicon substrate, wherein the silicon layer 104 is provided as the upper portion of the substrate 101, or is directly formed on the crystalline silicon of the substrate 101 by epitaxial growth. The semiconductor device 100 further comprises an implantation region 105 of a light inert species that is centered around a specified depth 106. It should be appreciated that the implantation region 105 may have a certain distribution in the vertical direction of
A typical process flow for forming the semiconductor device 100 as shown in
A gate insulating layer 113 is formed above the channel region 110 and separates a gate electrode 112 from the channel region 110. Spacer elements 111 are formed adjacent to sidewalls of the gate electrode 112 and metal silicide regions, such as nickel silicide, cobalt silicide and the like, may be formed on and within the gate electrode 112 and the drain and source regions 108. Finally, a stress-inducing region 115 is formed in the vicinity of the transistor element 150 and is mechanically coupled to the channel region 110, for instance via the gate electrode 112, and the drain and source regions 108. In the embodiment shown, the stress-inducing region 115 is provided in the form of a capping layer, which may also be used as an etch stop layer during a following process for etching contact openings to the drain and source regions and the gate electrode. For example, the stress-inducing region 115 may be comprised of silicon nitride that is formed to have a specified intrinsic, tensile or compressive stress.
A typical process flow for forming the device 100 as shown in
It should be appreciated that other process flows may be used in forming the drain and source regions 108 and the corresponding extension regions 109. For instance, disposable sidewall spacers (not shown) may be used to first form the deep source and drain regions 108 and then remove the disposable spacers prior to or after a corresponding anneal step to activate the dopants in the drain and source regions 108. Thereafter, the extension regions 109 may be formed and activated by an anneal process at a lower temperature. Afterwards, the spacers 111 may be formed. Irrespective of the process sequence used, during the implantation for the deep source and drain regions, possibly in combination with a pre-amorphization implantation, the light inert species in the implantation region 105 may be redistributed within the source and drain regions 108 or may even be at least partially driven out from the silicon region 104 during any anneal cycles for activating dopants in the source and drain regions 108 and the extension regions 109. At any rate, at least a portion of the implantation region 105 is maintained within the channel region 110 or in the vicinity thereof, when the implantation region is located in the insulating layer 103, wherein the specified depth 106 is substantially maintained although a certain broadening of the distribution around the depth 106 of the light inert species may take place during the various anneal cycles. Moreover, in some embodiments, a moderately high, that is, over-critical, concentration of the light inert species within the implantation region 105 may be provided and the species may already start creating bubbles or voids at the depth 106 during the dopant activation, similarly as bubbles are formed in an over-saturated fluid including a gaseous component upon occurrence of a disturbance.
Thereafter, the metal silicide regions 114 may be formed by depositing a refractory metal and initiating a chemical reaction with the underlying silicon in the drain and source regions 108 and the gate electrode 112. Thereafter, the stress-inducing region 115, for instance in the form of a capping layer or etch stop layer, may be formed, for example as a silicon nitride layer, wherein deposition parameters for forming the layer 115 may be adjusted to obtain a desired amount of tensile or compressive stress. As is readily known, silicon nitride may be deposited by a PECVD process, wherein one or more process parameters, such as the bias power, the temperature and the like, may be adjusted to obtain compressive or tensile stress within a wide range of approximately 0-800 MPa for tensile or compressive stress. During the formation of the metal silicide regions 114 and the stress-inducing region 115, again, elevated process temperature may possibly lead to a further generation of voids or bubbles within the implantation region 105, depending on the initially implanted concentration.
Based on the above considerations, a specified strain 117 may be induced within the channel region 110 by the stress-inducing region 115. As previously explained, the dislocation region 105 d weakens the mechanical coupling of the channel region 110 to the lower lying device regions, such as the insulating layer 103, thereby providing the potential that the channel or at least a portion thereof may more readily deform upon the application of an external force, such as that created by the stress of the layer 115, as is the case without the dislocation region 105 d. It should be appreciated that the finally obtained strain 117 may be controlled by adjusting the stress in the region 115 and in other stress-inducing regions that may be mechanically coupled to the channel region 110, such as the spacers 111 and the metal silicide regions 114, and by the parameters influencing the implantation region 105 or the dislocation region 105 d, such as the implantation parameters, the heat treatment parameters and the like. For example, the finally obtained strain 117 may be adjusted by selectively controlling the characteristics of the dislocation region 105 d at different areas of the semiconductor device 100. That is, for a given process flow for forming the transistor elements 150, one or more implantation parameters for forming the implantation region 105 may be varied to obtain a dislocation region 105 d having a different characteristic in different areas, thereby resulting in a different strain 117 at the different device areas.
With reference to
In other embodiments, the characteristics of the stress-inducing regions may be varied in different device areas to obtain a different amount of strain. Illustrative examples will be described with reference to
It should be appreciated, however, that the techniques for providing different strain at different device areas and/or for different transistor types described with reference to
It should be appreciated that, especially in the above-described embodiments of
Moreover, as previously described with reference to
Moreover, in some embodiments, the anneal cycles during the formation of a transistor element may be considered inappropriate with respect to a “premature” nano-void generation in respective implantation regions, such as the regions 105, 205 and 305. In this case, hydrogen may be implanted at a later manufacturing stage, for instance after completion of the drain and source regions. Hereby, the implantation energy may be selected to locate the hydrogen ions at a desired depth below the gate electrode, while the ions may penetrate deeply into the device region below the drain and source regions. The crystal damage caused by the hydrogen implantation may be negligible and may be cured during the heat treatment for forming the dislocation region from the implanted hydrogen ions.
As a result, the present invention provides a new technique that enables the formation of a dislocation region in the vicinity of a semiconductor region, the carrier mobility of which is to be adjusted by an external stress-inducing source. The dislocation region, which effectively reduces the mechanical coupling of the semiconductor region, such as a channel region, to adjacent device or substrate regions, may be formed by introducing a light inert species, such as hydrogen, into a specified device region and by an appropriate heat treatment to create a certain “separation” or micro-cleavage between the channel region and the lower lying device or substrate region. Therefore, an effective strain engineering may be enabled based on the dislocation region, wherein the strain obtained may be provided as tensile or compressive strain with a desired magnitude in that the characteristics of the dislocation region and/or the characteristics of the external stress-inducing source are correspondingly adjusted. Moreover, the strain may be adjusted differently for different device areas.
The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. For example, the process steps set forth above may be performed in a different order. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below.